Boulder scientist's study shows holes in Arctic ice melt predictions

Workshop next week at NCAR will focus on sea ice forecasts

Arctic summer sea ice, north of Alaska, as captured by a NASA satellite Sept. 13, when it reached its seaonal minimum. (Courtesy photo / NASA)

Forecasts of summer Arctic ice in recent years have registered some lukewarm results at a time when the demand for accurate projections is increasing, according to a new study led by a Boulder researcher.

A scientist at Boulder's National Snow and Ice Data Center is part of a team that analyzed 300 summer Arctic sea ice forecasts from 2008 to 2013, and found that forecasts are quite accurate when sea ice conditions track close to the downward trend observed in Arctic sea ice for the last 30 years.

But forecasts are not as accurate, they found, when sea ice conditions deviate higher or lower from the trend of recent decades.

While accurate shorter-term forecasts of summer ice in the Arctic are hard to make, there is strong interest in seeing those developed, as shrinking ice is a critical issue not only for the Arctic's coastal communities, but also resource extraction industries and commercial interests seeking a shortened shipping route between Europe and Asia.

"There is a lot of interest right now in what is going on up there," said Julienne Stroeve, a senior scientist at the National Snow and Ice Data Center and the lead author of the study, published recently in Geophysical Research Letters.

Those anxious to know better what to expect in the annual melt range from international industrial interests to hunters in local communities constricted by what ice conditions in their region will allow.

"The biggest people looking at this (are) the oil and gas companies and also shipping industries," said Stroeve, who recently accepted a full professorship at University College London.

In 2013, summer ice reached its annual minimum on Sept. 13 at 2.07 million square miles, according to the National Snow and Ice Data Center. That was 452,000 square miles below the 1981-2010 average extent. It was 664,000 square miles higher than the previous record low for the month, which occurred in 2012.

Stroeve and colleagues at the University of New Hampshire and University of Washington found that in years when the sea ice extent departed strongly from the trend, such as in 2012 and 2013, predictions on September sea ice extent failed, regardless of the forecast method utilized.

"What was most striking here is that in some years the predictions were very good, and the median of the predictions was very close to the real value, and in other views it was nowhere near it," said Lawrence Hamilton, a study co-author and sociology professor at the University of New Hampshire, who focused on the data analysis. "It was bimodal — mostly good, or mostly not-so-good, and that was a very interesting finding."

The study analyzed forecasts from the Study of Environmental Arctic Change Sea Ice Outlook, a project that gathers and summarizes sea ice forecasts made by sea ice researchers and prediction centers. Contributors to the SEARCH Sea Ice Outlook project employ a variety of techniques to forecast the September sea ice extent.

"We did not look at individual (forecast) techniques," Stroeve said. "It was more looking at an ensemble of everything that was sent in, rather than seriously evaluating every prediction."

She noted that better data on ice thickness and concentration entering the summer melt season, as well as improved forecasting of of summer atmospheric conditions in the Arctic, are both factors that could improve summer ice forecasting.

Stroeve said she believes accurate short-term predictions are available, "but challenges remain in predicting anomalous years, and there is a need for better data for initialization of forecast models,"

Boulder will play host to those focused on advancing sea ice prediction Tuesday and Wednesday when up to 60 scientists working in that field descend on the National Center for Atmospheric Research for the 2013 Sea Ice Prediction Workshop.

"I'll give a presentation about this paper just to start the discussion," Hamilton said. "It highlights things that we're doing well, and some other areas that need improvement. And that's exactly what scientists need to know about."

One outcome Stroeve hopes for out of the conference is to develop "a coordinated set of experiments or hind-cast evaluations going back in time, and seeing how well these various forecasting techniques work, so we can better understand the areas where improvements should be focused on."

The National Science Foundation and the Office of Naval Research supported the study.

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